Hominini


The Hominini, or hominins, form a taxonomic tribe of the subfamily Homininae. Hominini includes the extant genera Homo and Pan, but excludes the genus Gorilla.
The term was originally introduced by John Edward Gray, long before any details on the speciation of Pan and Homo were known. Gray's tribe Hominini by definition includes both Pan and Homo. This definition is still adhered to in the proposal by Mann and Weiss, which divides Hominini into three subtribes, Panina, Hominina, and Australopithecina.
Alternatively, Hominini is taken to exclude Pan. In this case, Panini may refer to the tribe containing Pan as its only genus.
Minority dissenting nomenclatures include Gorilla in Hominini and Pan in Homo, or both Pan and Gorilla in Homo.

Terminology and definition

By convention, the adjectival term "hominin" refers to the tribe Hominini, while the members of the subtribe Hominina are referred to as "homininan". This follows the proposal by Mann and Weiss, which presents tribe Hominini as including both Pan and Homo, placed in separate subtribes. The genus Pan is referred to subtribe Panina, and genus Homo is included in the subtribe Hominina. However, there is an alternative convention which uses "hominin" to exclude members of Panina, i.e. either just for Homo or for both human and australopithecine species. This alternative convention is referenced in e.g. Coyne and in Dunbar. Potts in addition uses the name Hominini in a different sense, as excluding Pan, and uses "hominins" for this, while a separate tribe for chimpanzees is introduced, under the name Panini. In this recent convention, contra Gray, the term "hominin" is applied to Homo, Australopithecus, Ardipithecus, and others that arose after the split from the line that led to chimpanzees ; that is, they distinguish fossil members on the human side of the split, as "hominins", from those on the chimpanzee side, as "not hominins".

Cladogram

This cladogram shows the clade of superfamily Hominoidea and its descendent clades, focussed on the division of Hominini. The family Hominidae comprises the tribes Ponginae, Gorillini and
Hominini, the latter two forming the subfamily of Homininae. Hominini is divided into Panina and Australopithecina. The Hominina are usually held to have emerged within the Australopithecina. Genetic analysis combined with fossil evidence indicates that hominoids diverged from the Old World monkeys about 25 million years ago, near the Oligocene-Miocene boundary.
The most recent common ancestors of the subfamilies Homininae and Ponginae lived about 15 million years ago. In the following cladogram, the approximate time the clades radiated newer clades is indicated in millions of years ago.

Evolutionary history

Both Sahelanthropus and Orrorin existed during the estimated duration of the ancestral chimpanzee-human speciation events, within the range of eight to four million years ago. Very few fossil specimens have been found that can be considered directly ancestral to genus Pan. News of the first fossil chimpanzee, found in Kenya, was published in 2005. However, it is dated to very recent times—between 545 and 284 thousand years ago. The divergence of a "proto-human" or "pre-human" lineage separate from Pan appears to have been a process of complex speciation-hybridization rather than a clean split, taking place over the period of anywhere between 13 Mya and some 4 Mya. Different chromosomes appear to have split at different times, with broad-scale hybridization activity occurring between the two emerging lineages as late as the period 6.3 to 5.4 Mya, according to Patterson et al., This research group noted that one hypothetical late hybridization period was based in particular on the similarity of X chromosomes in the proto-humans and stem chimpanzees, suggesting that the final divergence was even as recent as 4 Mya. Wakeley rejected these hypotheses; he suggested alternative explanations, including selection pressure on the X chromosome in the ancestral populations prior to the chimpanzee–human last common ancestor.
Most DNA studies find that humans and Pan are 99% identical, but one study found only 94% commonality, with some of the difference occurring in noncoding DNA. It is most likely that the australopithecines, dating from 4.4 to 3 Mya, evolved into the earliest members of genus Homo. In the year 2000, the discovery of Orrorin tugenensis, dated as early as 6.2 Mya, briefly challenged critical elements of that hypothesis, as it suggested that Homo did not in fact derive from australopithecine ancestors. All the listed fossil genera are evaluated for:
  1. probability of being ancestral to Homo, and
  2. whether they are more closely related to Homo than to any other living primate—two traits that could identify them as hominins.
Some, including Paranthropus, Ardipithecus, and Australopithecus, are broadly thought to be ancestral and closely related to Homo; others, especially earlier genera, including Sahelanthropus, are supported by one community of scientists but doubted by another.